Skillful seasonal predictions of extended summer drought and fire risk from southern Europe to the Middle East

The present study uncovers the capability of the ECMWF SEAS5 seasonal forecasting system to skillfully forecast the May-to-September Standardized Precipitation Evapotranspiration and Fire Weather indices (SPEI, FWI) in southern Europe and the Middle East, considering the unique verification period available for this system (1981-presence). This capability is visible in essentially all standard skill metrics (deterministic and probabilistic) up to a lead-time of six months and is particularly strong over the Iberian Peninsula, western France, northern Africa, the Near and Middle East, and in the regions surrounding the Black and Caspian Seas. Although the skill mainly resides on the correct reproduction of the long-term trend caused by anthropogenic warming, there is some skill for the detrended inter-annual time series pointing to the model’s capability to forecast internal climate variability. We also explore possible low-frequency skill modulations associated with distinct ENSO phases and model deficiencies diagnosed with the Ratio of Predictable Components, the latter measuring whether the ensemble’s spread and/or signal strength are realistic.